Piano action bushing assembly



March 1966 T. D. STEINWAY PIANO ACTION BUSHING ASSEMBLY Filed March 5, 1962 FIG- 4 M R W m s m E R G D O E H T BY Mar a/1 Fwm @Mm 4 W ATTQRN EYS United States Patent Oflflce 3,240,095 Patented Mar, 15, 1966 3,240,095 PIANQ ACTION BUSHING ASSEMBLY Theodore ll). Steinway, New York, N.Y., assignor to Steinway dz Sons, a corporation of New York Filed Mar. 5, 1962, Ser. No. 177,399 6 Claims. (Cl. 84-251) This invention relates to bearings, more particularly to bearings between parts made of wood or equivalent materials subject to swell and shrink due to changes in atmosphere conditions. This invention is of utility especially in connection with the pivotal connections in a piano action, ie the centers on which the action members swing back and forth, the same serving to illustrate this invention in the accompanying drawings.

Of the drawings:

FllGv 1 is a vertical fore and aft fragmentary section of the front portion of a grand piano showing one of the keys and hammer actions in side elevation to indicate the pivotal points to which the improved bearing of this invention is applicable with advantage;

FIG. 2 is a fragmentary plan view on a larger scale of the forked end of the hammer shank and its flange of FIG. 1, designated by the same numerals of FIG. 1, connected by the improved bearing of this invention;

FIG. 3 is a fragmentary view partly in section and on a still larger scale of the improved bearing of FIG. 2 to illustrate the configuration and arrangement of the bearing bushings; and,

FIG. 4 is a view in end elevation of one of the bearing bushings of FIG. 3.

The piano construction shown in FIG. 1 is any usual construction and it will suffice to point out the main parts, as follows: key-bed ll, key 2, hammer 3, hammer shank 4, hammer flange 5, flange rail 6, pivotal connection '7 between hammer shank 4 and hammer flange 5, wippen S, wippen pivot 9, jack fly 10, pivot 11 between wippen and jack fly, repeating lever 12, and pivot 13 between wippen and repeating lever.

The aforesaid numerals 7, 9, l1 and 13 designate the pivotal connections in FIG. 1 in which the improved bearing of this invention is useable to advantage and are representative of such pivotal connections in piano actions, grand or upright. Since all of these bearings have the same construction, bearing 7 only is illustrated in FIGS. 2, 3, and 4.

An object of this invention is to provide an improved bearing between parts such as the aforesaid, which, especially in the case of piano actions, will enable the relatively large clearance heretofore required between mating action parts, to be reduced substantially or even eliminated entirely, or the parts placed in compression, without having to increase the force necessary to move the parts on the action center and with assurance that the center will work freely, despite any distortion of the wood parts caused by extreme climates.

The action consists of a series of levers, usually made of wood, which are pinned together at certain hinge points of so-called centers. These connections are usually effected with a tongue-and-fork arrangement held together by means of a lateral or transverse pin. These pins are generally of German silver with considerable nickel content so that they will not corrode, and are very accurately manufactured with tolerances on diameter and concentricity. The pin is held firmly in the central or tongue member, as the hole is drilled for an interference fit. The fork member revolves around the pin and is provided with a bushing, in order to achieve a noiseless, eflicient and durable action.

This bushing is commonly made of bushing cloth, a special all-wool felted fabric especially designed and manufactured for this purpose. it has resilience and softness sufiicient to eliminate noises, and to absorb impacts in order to eliminate failure of the action parts through fracture and maintain accurate alignment of the parts.

However, this material is hygroscopic, tending to swell in moist atmospheric conditions and shrink in dry conditions. As a result, with moist conditions the center often becomes so tight that its function is hindered or rendered impossible and the corresponding piano key either loses all speed and sensitivity of action or fails to function entirely. Conversely, with dry conditions the centers will occasionally become too loose, resulting in rattles in the action and inaccuracy in the alignment of parts, with consequent loss of power and control in the so-called touch qualities of the action.

It is therefore another object of this invention to eliminate these costly disadvantages through the provision between the mating action parts of a new, useful and improved one-piece bushing of a suitable plastic or elastomeric material. Other and further objects of this invention will appear from the following description, the accompanying drawings and the appended claims.

In accordance with this invention, the bushing is provided with an integral annular flange or tab at one end, which is positioned on the internal or tongue side of each arm of the fork member. The bushing is inserted from the inside into a bushing hole of correct size to afford a light push fit, so as to eliminate any possible distortion of the internal diameter. The flange prevents any possible movement of the bushing outwards Further, with the proper fit, no movement whatsoever, either rotary or inwards towards the tongue member, occurs in over 8,000,000 cycles, which is the approximate equivalent of 40 years of hard use. Thus the provision of a screw thread or an annular or longitudinal milling or grooving or embossing or texturing or etching or gluing or cementing or other method of holding the bushing in place is unnecessary. Elimination of the necessity for gluing the bushing in place obviates the risk of loose and thus noisy and inaccurate bushings, and of glue-soaked bushings, and of bushings uneven in their action because of the inequitable distribution of glue. Since the bushings are inserted individually, no unevenness results from uneven wear of bushing cloth, eliminating the jerking movements sometimes experienced with conventional bushings.

The flange also stiffens the bushing, preserving it against deformation by the impacts incident in its use.

The flange also acts as a spacer, providing the necessary clearance between the mating parts.

It further provides a small area of contact between the mating parts, should they move into contact, and since the flange is made of, preferably, a low-friction material, the amount of friction between the parts is materially reduced from that of the previous wood-onwood contact. The provision of a raised ring around the inner circumference of the flange in order to still further lessen friction has not proved to have significant advantage. This results in a freer, lighter action, requiring less effort to play.

Since, in addition, the bushing contains no fibers to loosen up, the ring machined on the tongue member becomes unnecessary, which allows a considerable simplification in the manufacture of the action parts and materially reduces the expense of manufacture.

Referring now more particularly to the accompanying drawings which form part of the instant specification and on which like numbers refer to like parts throughout the several views, the bearing 7 comprises a cylindrical metal pin having tight or driven fit with a hole extending laterally through the tongue portion 16 of the wooden hammer flange 5, both ends of the pin projecting beyond the sides of the tongue to form trunnions. These trunnions are surrounded by cylindrical bushings 17 of a suitable plastic or elastomeric material, preferably a fluorocarbon resin such as polytetrafluoroethylene under the trademark Teflon, these bushings being respectively located and retained stationarily in holes provided to receive them in the wooden arms 18 of the formed end of the hammer shank 4. The bushings are inserted from between the arms 13 into these holes which are of correct size to afford a light push fit, so as to eliminate any possible distortion of the internal diameter. Thus, the hammer shank is pivoted to the tongue portion 16 of the hammer flange 5, the bushings 1'7 turning about the trunnion ends of the metal pin 15.

The outer end of each bushing is preferably slightly chamfered as at 19 to facilitate ease of insertion of the bushing in the bushing hole. However, the inner end of each bushing is provided with an integral annular flange or tab 20 which abuts against the opposing arm 18 of the forked end of the hammer shank. The flange 20 stiifens the bushing, preserving it against deformation by the impacts incident in its use, and also acts as a spacer between the associated arm 18 and the tongue portion 16 of the hammer flange, providing the necessary clearance between the mating parts.

Further, it has been found that where previously a clearance between the mating parts of .015" or more was ad visable, it is now practicable to reduce this to .005 or even to 0, with actual contact of the flange 20 and the tongue member 16, without increasing the force necessary to move the parts, as measured with a sensitive force gage. In fact, it has been found that with a suitable low-friction material, considerable actual compression of the partsin effect a negative clearance-is necessary before the center becomes tighter so as to inhibit its free working. Thus the center works freely, despite distortion of the wood parts caused by extreme climates.

The thickness of the flange 20 guarantees the necessary spacing between the mating parts 16 and 18 and reduction or elimination of any further clearance is now possible. This is of advantage because it allows the thickness of the tongue member 16 and the fork arms 18, preferably the latter only, to be increased somewhat, thereby adding strength to the parts. Also the effective length of the pin 15 and bushing 17 contact or journal bearing is increased, yielding gains in the solidity of the center and accurate alignment of the parts. Regulation of the action-for instance, control of the impact of the hammer of a grand piano on the three strings comprising a note in the treble section-gains in accuracy, solidity and durability.

The bushings 19 may be molded or lathe-cut or sintered or fabricated in any suitable manner. It is preferable to manufacture them on automatic screw machines as this affords a more accurate result. For instance, the variation in internal diameter between bushings can be held to a thin .001", that is, to slightly less than .001 so that variations become insignificant and sizing or ream- 4. ing as with bushing cloth is unnecessary, resulting in manufacturing economies.

Further economies result from a reduction in the manufacturing steps necessary since one operation-insertion of the bushing 17-replaces the twelve to fifteen operations necessary with bushing cloth. Furthermore, waste rate drops from around 65 to practically zero.

The bushing 17 may be manufactured from any material of the necessary resilience or non-rigidity and with the desirable non-hygroscopic qualities combined with the strength properties, stability, abrasion-resistance and frictional qualities found in bushing cloth or better. Good results are available with polyethylene or other polyolefins, vinyl, nylon, rubber and other materials and copolymers, particularly when compounded with a lubricant such as graphite or molybdenum disulfide. However, it is preferable to use a fluorocarbon resin such as polytetrafluoroethylene under the trademark Teflon, or a similar fluorinated hydrocarbon since the desired qualities are at a maximum with these materials and combine well with the configuration of the bushing to give several advantageous results.

In a piano action, indicated loads on the centers are very light compared to those on hearings in general, being generally well under 10 p.s.i. (pounds per square inch). Speeds are also comparatively very low, the maximum being under 10 f.p.m. (feet per minute). This results in a low PV factor, or pressure-velocity factor, in the range of 50 to 100, so no unusually high strength properties in the bearing material are required.

Hygroscopic properties of the fluorocarbon resins are excellent, moisture absorption being flat zero in contrast to other plastic materials and to bushing cloth bushings which, at a given temperature, pick up 8% moisture content by weight with a change in relative humidity from 25% to In comparative trials with piano actions in a moderate high humidity environment, centers equipped with this invention showed no increase in the force necessary to actuate them, whereas centers equipped :with bushing cloth bushings, showed an increase of 65% in this force, and. failed to function properly because of excessive tightness. In a piano this would result in a sticking key.

In similar trials in a moderate low humidity environment, centers equipped with bushings 17 of this invention were still firm and solid. Centers equipped with bushing cloth bushings lost 16%, and looseness or side play was evident in many cases. In a piano this looseness creates squeaks and noises and results in inaccurate alignment of parts and ineflicient control and. operation. The piano is said to be out of regulation.

Soaking in water an action part equipped with bushings of this invention resulted in no significant effect other than a temporary reduction in the effort needed to actuate the center. A bushing cloth bushing failed through swelling and through destruction of the glue line. Water vapor will actually have a lubricating effect on the bushing of this invention, making the center act more freely.

Thus the bushing of this invention will remain freeacting but firm in all normal climates and afford a reliable, efl'icient performance which is not available with conventional actions.

Resilience of fluorocarbon resin bushings made of Teflon is ideal for the purpose, with a hardness of Shore D 50/56 or Rockwell R58, and with a springy, yet tough consistency. A polymeric amide resin bushing made of nylon, for instance, is about twice as hard and its deformation under load about fifty times greater. Thermosetting resins have proved. to be too hard and brittle, failing under repeated impact. The bushing of this invention remains noiseless, solid and yet free in use. It is not necessary to use a foamed or porous material. Also the vibration damping qualities are excellent at all frequencies, which is very desirable in a reciprocating system with impact stresses.

Abrasion resistance of the bushing of this invention has proved excellent, with no perceptible wear or looseness in use.

Extensive testing of the fluorocarbon resin bushings in concert pianos in almost daily use and trials on a testing machine for over 8,000,000 cycles confirm their performance. The bushing remain resilient, noiseless, with no side play or rattle or flat spots, and yet free and solid. in movement.

Frictional qualities of the fluorocarbon resin bushing are excellent as fluorocarbon resins have an extremely low coefficient of friction, generally quoted as .04, with a range from .02 to .40. This is far superior to wool bushing cloth which is five times greater than the generally quoted value, approximately .22. Recent comparative figures give a coefficient six times greater than .04 for polyethylene and Nylon and nine times greater for polyvinyl chloride. This low friction is constant at .increasing humidities and temperatures over freezing, while other materials are generally adversely influenced. This affords a reduction of friction losses in the operation of the action so that the key will return faster to its playing position, resulting in a faster and more responsive action, more efiicient in operation and affording a more sensitive control. Bushing cloth centers can be made very freeacting but only by making a very loose fit of the bushing on the pin, with its attendant dangers of noise, misalignment, loss of power and of proper accurate function.

The low-friction bushing of this invention requires no lubrication, thus eliminating the disadvantages of oil lubricants which tend to attract dirt and gum up, andv of soap of glycerine-base lubricants which tend to attract moisture, corrode the pin and swell the bushing.

The low-friction bushings of this invention further afford an improved, sensitive, smoother action because the material has a static coeflicient of friction equal to its dynamic coefiicient of friction or less. Thus no breakaway effort is needed to start the center in motion and there is no stick-slip during operation. This is very desirable in a reciprocating system with a start and stop in each cycle of operation. Squeaks experienced with other materials do not occur.

The low-friction bushing of this invention further allows a reduction of clearances between the parts which may now operate in contact without loss of performance and which permits sturdier parts with a more accurate operation as mentioned above.

The bushing has considerable further advantages through the lack of cold flow or rheological properties. Though Teflon as a bushing material is very stable compared to other materials that exhibit creep or deformation under long continued static load, the bushings of this invention exhibit a conformability or incomplete recovery from compressive stress which, in combination with its low-friction properties, is very advantageous. It has been found that an interference fit of up to .004 between the pin and the housing produces no significant effect in the freedom of action of the center. Thus the tedious and costly sizing of the pin hole is unnecessary, with consequent savings in manufacture and in repair work during the life of the instrument. In fact, interference fits of greater degree have no practical significance. It has been found that the mechanical force or effort necessary to actuate the center at the time of pinning soon drops to 50% or 60% of the original figure, though the center remains solid and without side play.

Thus it will be seen that the objects of this invention have been accomplished and the bushing thus enables the production of an action center virtually free from maintenance problems. Easing, repinning and lubrication become unnecessary. This is expensive service because skill, time and experience are needed. This money is saved in the factory, in the store, and in the home. The bushing thus provides a reliable, durable and efficient service throughout the lift of the instrument. This is a 6 great advantage over the previous practice, particularly so because of the difliculty of getting competent service on pianos and the tendency of owners to neglect the need for this servicing.

What is claimed is:

1. A piano action assembly comprising in combination with pivotally connected wood parts spaced apart to provide opposed surface portions, a pivotal connection between said parts comprising a metal pin fixedly carried by one of said parts and projecting therefrom to provide a trunnion end portion, said trunnion end portion being journalled in and surrounded by a bushing of a substantially non-hygroscopic, resilient, inert elas-torneric material exhibiting a lack of cold flow under long-continued static load and possessing a low coeflicient of friction in the range of from 0.02 to 0.40, said bushing being seated, with a light push fit, in a hole in another of said parts, said bushing having an integral annular spacing and supporting flange disposed in the space between said parts, and said flange having its opposite annular surface portions in substantially close-fitting surface engagement with said opposed surface portions of said pivotallyconnected parts.

2. A piano action assembly in accordance with claim 1 in which said bushing material is a fluorocarbon resin.

3. A piano action assembly in accordance with claim 2 in which said fluorocarbon resin is polytetrafluoroethylene.

4. A piano action assembly in accordance with claim 1 in which said annular flange is under compression between said opposed surface portions of said pivotallyconnected parts.

5. A piano action assembly comprising in combination with a piano action member having fork arms and a piano action member having a tongue portion disposed between and in spaced relation to said fork arms to provide opposed surface portions at opposite sides of said tongue portion, a pivotal connection between said tongue portion and said fork arms comprising a metal pin traversing and fixedly carried by said tongue portion and projecting from opposite sides of said tongue portion, to provide a trunnion end portion at each of said opposite sides, said trunnion end portions each being journalled in and surrounded by a bushing of a substantially non-hygroscopic, resilient, inert elastomeric material exhibiting a lack of cold flow under long-continued static load and possessing a low coeflicient of friction in the range of from 0.02 to 0.40, said bushings each being seated, with a light push fit, in a bushing hole in the respective fork arms, said bushings each having an integral annular spacing and supporting flange, said flanges being disposed, at opposite sides of said tongue portion between said tongue portion and said fork arms, and the respective flanges each having their annular surface portions in substantially close-fitting surface engagement with opposed surface portions of said tongue portion and the associated fork arm.

6. In a piano action, the combination with a bifurcated action member and a tongued action member having its tongue disposed between the arms of said bifurcated action member and in spaced relation thereto to provide opposed surface portions at opposite sides of said tongue, of a pivotal connection between said arms and said tongue comprising axially aligned bushings frictionally received in said arms with a light push-fit, said bushings each having an integral annular flange at one end, said flanges being disposed at opposite sides of said tongue between said tongue and said fork arms and spacing said tongue from said arms, the respective flanges each having their annular surface portions in substantially close-fitting surface engagement with opposed surface portions of said tongue and the associated fork arm, said bushings being made of a substantially non-hygroscopic elastomeric material exhibiting a lack of cold flow under long-continued static load and possessing a low coefficient of friction in the range of from 0.02 to 0.22 and, a bearing pin fixedly 7 8 secured to said tongue and journalled in said bushings 2,951,053 8/1960 Reuter et 211. with an interference fit of up to 0.004". 2,9 4,341 12/ 1960 Doyle et a1.

3,011,219 12/1961 Williams. References Cited by the Examiner 3,096,128 7/ 1963 Wight.

UNITED STATES PATENTS 5 FOREIGN PATENTS 1,294,956 2/1919 Schou. 1,260,046 3/1961 France. 1,613,768 1/1927 Perrot. 707,111 4/1954 Great Britain. 2,615,763 10/1952 Wolford. I 2,641,828 /1953 Knoblaugh 3O8 238 X 10 DAVID J. WILLIAMOWSKY, Przmary Examiner. 2,831,737 4/ 1958 Jacoby. MILTON KAUFMAN, ROBERT C. RIORDON,

2,871,562 2/1959 Kern. Examiners. 

6. IN A PIANO ACTION, THE COMBINATION WITH A BIFURCATED ACTION MEMBER AND A TONGUED ACTION MEMBER HAVING ITS TONGUE DISPOSED BETWEEN THE ARMS OF SAID BIFFURCATED ACTION MEMBER AND IN SPACED RELATION THERETO TO PROVIDE OPPOSED SURFACE PORTIONS AT OPPOSITE SIDES OF SAID TONGUE, OF A PIVOTAL CONNECTION BETWEEN SAID ARMS AND SAID TONGUE COMPRISING AXIALLY ALIGNED BUSHINGS FRICTIONALLY RECEIVED IN SAID ARMS WITH A LIGHT PUSH-FIT, SAID BUSHINGS EACH HAVING AN INTEGRAL ANNULAR FLANGE AT ONE END, SAID FLANGES BEING DISPOSED AT OPPOSITE SIDES OF SAID TONGUE BETWEEN SAID TONGUE AND SAID FORK ARMS AND SPACING SAID TONGUE FROM SAID ARMS, THE RESPECTIVE FLANGES EACH HAVING THEIR ANNULAR SURFACE PORTIONS IN SUBSTANTIALLY CLOSE-FITTING SURFACE ENGAGEMENT WITH OPPOSED SURFACE PORTIONS OF SAID TONGUE AND THE ASSOCIATED FORK ARM, SAID BUSHINGS BEING MADE OF A SUBSTANTIALLY NON-HYGROSCOPIC ELASTOMERIC MATERIAL EXHIBITING A LACK OF COLD FLOW UNDER LONG-CONTINUED STATIC LOAD AND POSSESSING A LOW COEFFICIENT OF FRICTION IN THE RANGE OF FROM 0.02 TO 0.22 AND, A BEARING PIN FIXEDLY SECURED TO SAID TONGUE AND JOURNALLED IN SAID BUSHINGS WITH AN INTERFERENCE FIT OF UP TO 0.004". 